1. Field of the Invention
The present invention relates to an optical processing method usable preferably in the fields of optical communication systems and optical information processing, and a waveguide type optical device for optical processing that can be used preferably in this method.
2. Description of the Prior Art
The main practical methods known for optical processing are mechanical methods, and methods which rely on the phenomenon that the refractive index of a light transmitting medium changes when non-mechanical energy such as voltage, electric current or heat is applied to the light transmitting medium. Currently, the former methods are put to practical use. Of the latter methods, the most feasible one uses the electro-optical effect of lithium niobate (Pockels effect, an effect in which the birefringence characteristics of the material change according to an electric field). Recently, devices using the electro-optical effect of dye attached polymers, which are much more processable and much less expensive than lithium niobate have been developed (A. J. Ticknor, G. F. Lipscomb, and R. Lytel, Proc. SPIE Vol 2285, 386 (1995). These devices have posed the problem of long-term stability. With such devices, the use of materials undergoing great changes in the refractive index at low voltage is advantageous for low voltage driving as well as for the realization of miniaturized high density devices. The magnitude of a change in the refractive index of lithium niobate per unit voltage is an index to evaluating the feasibility of the material.
A method using the refractive index anisotropy of a liquid crystal is also known for optical processing, which method utilizes changes in the refractive index by application of voltage. The use of liquid crystal produces only a slow response (several tens of microseconds to several milliseconds) compared with a response obtained by use of the Pockels effect of lithium niobate or the like (nanoseconds). Liquid crystal, however, is advantageous in that it generally undergoes a large change in the refractive index when voltage is applied. Optical devices taking this advantage, such as optical switches, have also been developed. Most of them are vertical type devices, and waveguide type optical devices have been minimally studied. The reason why a practical waveguide type optical device using a liquid crystal has not been developed is that a liquid crystal is subject to regular or irregular deformations or fluctuations in the orientation vector that occur on the scale of about the wavelength of light. This causes scattering of light, and a great optical transmission loss. Another reason is the fluidity and poor processability of liquid crystal.